1. Field of the Invention
The present invention generally relates to pumpjack dynamometers and, more particularly, to apparatus and methods for producing and transmitting dynamometer card information.
2. Description of the Background
Dynamometers are commonly utilized in the oil field to monitor the operation of pumpjacks used to pump oil to the surface. A dynamometer card provides information related to pumping conditions as is described in detail in subsequently listed patents. For instance, a typical use of such information involves determining when a well has reached what is known as a pump off condition wherein the wellbore does not receive enough oil to fill the downhole pump during the entire pump stroke. Changes in the dynamometer card readings over time may be used to provide this information. It may be desirable to temporarily stop operating the pump until the pump off condition has been obviated by continued flow from the formation into the wellbore while the pump is shut down. Pumpoff control techniques are known to improve field development efficiency and reduce maintenance costs.
Change in the dynamometer card readings over time is one of the more important uses of dynamometer card information. Consistency over time in the way measurements are taken is important for this use of dynamometer card information. Consistency requires that calibrations remain constant and do not change over time, as has been a problem with many prior art devices. It would be desirable to have a sensor that does not require time consuming initial calibration procedures, that automatically calibrates itself, and that continuously recalibrates itself so that one may be assured that changes in dynamometer card information over time are due to changes in the well rather than changes in the calibrations.
Various sensors are provided in the prior art for determining the position of the walking beam of the pumpjack. Potentiometers, reed switches, and other types of switches have been used in the past in order to supply signals indicative of the position of the walking beam. The problem with such position sensing devices is that they are usually subject to wear, require careful initial calibration, require maintenance including regular recalibrations, and may not always provide accurate or reliable information. Hydrogen sulfide gas is often present in the vicinity of the pump jack, and that gas adversely affects the reliability of much of this sensing equipment. Well personnel working on the pumpjack may inadvertently loosen or change components in such a way that calibrations are affected. Prior art equipment for sensing the position of a walking beam is frequently mounted on the walking beam at a location where it is highly susceptible to weather conditions such as variable temperature, and may have reduced reliability due to temperature drift errors. Minor irregularities or mechanical jitters in movement of the walking beam may also cause spurious or repeatable errors.
As the dynamometer data is produced, various techniques are used to collect and use the data, some of which require expensive sensors, some of which may be less reliable over time, and some of which may require significant maintenance for calibration requirements. It would be desirable to provide methods for sampling dynamometer card information that may be used to monitor well conditions over time at less cost with improved reliability.
Once data is collected, radio transmitters have been used in the past to transmit the data to another location. However, in some areas the use of radio transmitters is not allowed. Where radio transmitters are allowed, it is often difficult to obtain additional channels for transmission. As well, FCC rules must be followed and may require radio transmitters to be installed according to certain specifications that may limit their usefulness for some purposes. Infrared transmitters have limited usefulness in sunlight due to ambient infrared noise that results in a short transmission distance if operation is possible at all. As well, infrared transmitters have limited selectivity and may have problems for use with closely spaced wells where multiple transmissions may occur.
The following patents discuss the aforementioned background and problems in some depth along with previous solutions to the many problems encountered in this area:
U.S. Pat. No. 4,363,605, issued Dec. 14, 1982, to Manuel D. Mills, discloses an apparatus for generating an electrical signal which is proportional to the tension in a bridle that supports a string of sucker rod associated with a pumpjack unit.
U.S. Pat. No. 5,458,466, issued Oct. 17, 1995, to Manuel D. Mills, discloses an apparatus and method for minimizing fluid pounding in a pumpjack by dictating the length of the run cycles of the pumpjack.
U.S. Pat. No. 4,631,954, issued Dec. 30, 1986, to Manuel D. Mills, discloses an improved pump control having a device for measuring relative movement between structural components of a pumpjack, and converting the movement into a signal which varies according to the magnitude of the movement.
U.S. Pat. No. 4,873,635, issued Oct. 10, 1989, to Manuel D. Mills, discloses a pump off control device for controlling a pumpjack unit. The device measures the length of time required for the pump to downstroke successive numbers of times. When the time differential reaches a predetermined value, the well is shut in for a time interval.
U.S. Pat. No. 4,492,029, issued Jan. 8, 1985, to Tanaka et al., discloses an inclinometer comprising a sector weight pivotally supported on a main body which may become inclined. The weight is relatively rotatable with respect to the main body and constantly hanging vertically due to gravity regardless of an inclination of the main body. A code part and a detecting part produces a detection output based on the predetermined code according to the inclination of the angle of the body.
U.S. Pat. No. 4,584,778, issued Apr. 19, 1986, to Komasaku et al., discloses an angle change indicator comprising a pair of opposing magnets, a sector-shaped pendulum made of an electro-conductive non-magnetic material and pivotal past a spacing between the opposing magnets, and a pair of photo sensors disposed on both side edges of the pendulum.
U.S. Pat. No. 4,467,527, issued Aug. 28, 1984, to North et al. discloses a digital level that includes a digital display for displaying the angle of inclination between a straight edge of a digital level and a desired reference plane. An alarm is also included to indicate whenever the digital level is held parallel to a desired reference plane.
U.S. Pat. No. 4,716, 534, issued Dec. 29, 1987, to Baucom et al., discloses an angle finder with a rotatably mounted disc on which is mounted a weight. The disc has markings that represent two degrees of arc. Three photo detectors sense the movement of the markings and a microprocessor determines angular alignment of the reference surface.
U.S. Pat. No. 4,798,087, issued Jan. 17, 1989, to Takeda et al., discloses an inclination detector of a generally fan shaped detector having a plurality of slits formed therein concentrically at intervals, and a light emitting element and a light sensitive element constituting a photo coupler disposed on opposite sides of the displacement detection plate.
U.S. Pat. No. 4,811,492, issued Mar. 14, 1989, to Kakuta et al., discloses a cant angle sensor assembly that includes a pendulum pivoted on a supporting system adapted to be mounted on an object whose cant angle is to be sensed for swinging movement in a direction of the tilt of the object. A moveable electrode is provided on the pendulum and has a first and second movable electrode plate, and a first stationary electrode plate is fixedly mounted on the supporting system in an opposed relation.
U.S. Pat. No. 4,922,620, issued May 8, 1990, to E. Terragni, discloses a device for determining the inclination of a plane with respect to a theoretical horizontal plane wherein an inclination detector element is rotatably associated with a box like body. Light detectors determine the position of the detector element with respect to the base plane based on coded slits therein.
U.S. Pat. No. 4,942,668, issued Jul. 24, 1990, to R. C. Franklin, discloses a digital inclinometer for detecting the angular orientation of a structure that includes a rotatable encoding disk on which is mounted a horizontal tilt sensor. The inclinometer electronically measures, by angular indices on the encoding disk, the difference between the angular orientation of the device and a horizontal orientation.
U.S. Pat. No. 4,606,133, issued Aug. 19, 1986, to F. J. Mills, discloses an inclinometer for producing high resolution signals of inclination relative to various references. High resolution data signals are produced through the use of a digital encoding wheel which is suspended in equilibrium in a fluid to substantially eliminate frictional forces. A microprocessor, or state logic machine is used to analyze and process the data to provide various displays of inclination including an audible output.
U.S. Pat. No. 3,951,209, issued Apr. 20, 1976, to S. G. Gibbs, discloses a method for monitoring a rod pumped well and determining when the well has pumped off. The method uses a dynamometer to monitor the power input to the rod string and senses when the power input decreases to determine when the well pumps off.
U.S. Pat. No. 4,143,546, issued Mar. 13, 1979, to R. P. Wiener, discloses a device to determine the work done by a sucker rod pump using a pendulum potentiometer mounted on the walking beam of the pump and a load sensing pin located at the lower end of the wire line which is suspended from the horsehead. Meters mounted in a portable reading instrument show the maximum rod pull, the minimum rod pull, the stroke of the pump, and the area of the force-versus-stroke diagram. A display of the shape of the force-versus-stroke diagram may be given through the use of an X-Y plotter.
U.S. Pat. No. 4,483,188, issued Nov. 20, 1984, to McTamaney et al., discloses an apparatus for recording and subsequent playback of selected dynagraphs for well employing sucker rod pumping units to determine well faults which cause well shut down. Calibration data from well monitoring equipment is stored in a first endless tape type of memory during calibration of the well, and operation data from the monitoring equipment is stored in a second endless tape.
U.S. Pat. No. 4,509,901, issued Apr. 9, 1985, to McTamaney et al., discloses a method for detecting problems in sucker rod well pumps and for determining which type of problem occurs. A first transducer provides a signal representative of the load on a sucker rod string and a second transducer provides a signal representative of the sucker rod position. The load signal and position signal are used to generate a dynagraph of rod load vs rod position with the pump working normally.
U.S. Pat. No. 4,551,730, issued Nov. 5, 1985, to McTamaney et al., discloses a method for entering control points relative to a dynagraph of a well pumping unit using the position of a beam and pen holder of an XY plotter.
U.S. Pat. No. 4,561,299, issued Dec. 31, 1985, to Orlando et al., discloses an apparatus for detecting changes in inclination used to determine the position of the sucker rod of a sucker rod pump and includes a magnetic field sensor such as a linear output transducer to provide a linear output signal and a cantilever spring having a counterweight and magnet on its free end disposed adjacent to the linear transducer.
U.S. Pat. No. 4,583,915, issued Apr. 22, 1986, to Montgomery et al., discloses a pump off controller that checks for pump off by calculating the area inside of a figure whose boundaries are the minimum load.
U.S. Pat. No. 4,594,665, issued Jun. 10, 1986, to Chandra et al., discloses an apparatus for detecting fluid found in a sucker rod oil well, using values of sucker rod position and sucker rod load to calculate a reference position and a selected load value.
U.S. Pat. No. 4,817,049, issued Mar. 28, 1989, to Bates et al., discloses a data logging device with a data memory unit and a transducer interface unit.
U.S. Pat. No. 4,973,226, issued Nov. 27, 1990, to F. E. McKee, discloses a method of maintaining a substantially constant amount of filling of a liquid well pump actuated by a polished rod which is reciprocated by a prime mover.
U.S. Pat. No. 5,064,349, issued Nov. 12, 1991, to Turner et al., discloses a method of monitoring and controlling a pumped well having a rod string extending from a pumping unit.
U.S. Pat. No. 5,167,490, issued Dec. 1, 1982, to McKee et al., discloses a method of calibrating a well pump off controller for determining the average load during a pumping stroke.
U.S. Pat. No. 5,182,946, issued Feb. 2, 1993, to Boughner et al., discloses a device for use on a well pumping unit that provides for real time measurement and recording of acceleration of a polished rod resulting from the oscillating linear motion induced by the rotating motion of the pumping unit crank.
U.S. Pat. No. 5,224,834, issued Jul. 6, 1993, to Westerman et al., discloses an apparatus for controlling the operation of a rod pumped well.
U.S. Pat. No. 54,291,777, issued Mar. 8, 1994, to Chang et al., discloses a system for monitoring performance of a pumping unit of an oil well that includes a first sensor for measuring the inclination angle of a beam forming part of the pumping unit, a second sensor for measuring the load on the beam, and a third sensor for measuring the load on an electrical motor used in conjunction with the pumping unit.
U.S. Pat. No. 5,406,482, issued Apr. 11, 1995, to McCoy et al., discloses a device to produce a position trace for a pumpjack with stroke markers to indicate position of the rod during its cyclical operation using an accelerometer.
U.S. Pat. No. 4,541,274, issued Sep. 17, 1985, to J. C. Purcupile, discloses a device wherein pulses produced by a pulse generator coupled to the output shaft of an electric motor are counted by a computer to locate the polish rod at a series of positions during each reciprocation.
Although the above-listed patents address problems relating to position indicating sensors, they do not disclose highly reliable techniques for automatic calibration and recalibration of such devices to thereby substantially eliminate calibration errors that may otherwise distort dynamometer cards taken at different times using prior art devices. The present device also works to reduce or eliminate errors caused by mechanical jitter or variations in the walking beam movement through the pumping cycle. As well, the present invention provides apparatus and techniques to improve data collection techniques. Moreover, the present invention provides reduced manufacturing and operating costs.
Consequently, there remains a need for a lower cost, readily available, easily manufactured, quickly assembled, lower maintenance apparatus and methods for providing data used for producing dynamometer cards. Those skilled in the art have long sought and will appreciate the present invention that addresses these and other problems.